It is known to correct abnormal curvature of the spine and/or pathological inclinations between vertebrae by using longitudinal bars that are arranged on either side of the vertebral column and that are secured to the vertebrae by screws inserted in the vertebrae themselves or by hooks, e.g. inserted along the spinal canal.
Nevertheless, such screws and hooks have the disadvantages of being aggressive for the spine.
In order to mitigate those drawbacks, proposals have been made for a flexible elongate fastener element combined with an implant suitable for being secured to a longitudinal bar, the elongate element being fastened to the implant and engaging at least a portion of a vertebra by forming a loop about that portion.
The longitudinal bars can be used for treating sclerosis or indeed for treating degenerative pathologies. Various different levels of degeneration are encountered, e.g. involving one vertebra, such as discopathy, or two vertebrae, such as spondylolisthesis, or indeed several vertebral levels such as C- or S-sclerosis.
In such treatments, the longitudinal bar needs to be connected with the vertebral level for correction by using an elongate element, which passes around at least a portion of a vertebral body and around said bar with the ends of said elongate element possibly being held by means of a suture or a knot, or by using implantable connection means. By way of example, said connection means may comprise a housing receiving the longitudinal bar and the elongate element wound around the bar, together with clamping means for blocking the bar and said elongate element in said housing. In general, the clamping means comprise means that pinch said elongate element so as to prevent any movement thereof.
One of the problems that the present disclosure seeks to solve is putting the elongate element under tension when it forms a loop over at least a portion of a vertebral body, and is engaged with an implant and/or a longitudinal bar.
EP 1 933 743 B1 relates to a tensioning instrument for tensioning an elongate element comprising a movable cylindrical part suitable for moving in translation around a rod, said rod having bearing means at its distal end for bearing against a longitudinal bar and not against the implant that receives the bar the elongate element. The movable cylindrical part also includes a lug for fastening the elongate element. The torque clamping system can be actuated by means of a handle. The elongate element is tensioned by the surgeon pressing on the handle without limit on the tension that can be applied. No portion of the instrument is adapted to allow the elongate element to move, the element merely being tensioned between two points (i.e. the implant and the lug) and being put under tension without there being any movement of the elongate element in a portion of the instrument. With that clamping system, the surgeon can apply excessive tension on the elongate element, running the risk of spoiling the adjustment of the longitudinal bar(s) placed on the vertebral level(s) for correction, or indeed the risk of moving the vertebrae. In addition, the tension is applied on a loop in line with two free ends of the elongate element that are held together with a keeper. The tension that is applied is therefore not the same on both of the free ends since it is applied directly to only one free end of the elongate element that extends the other free end via the loop. Tension is thus applied in unbalanced manner on the free ends of the elongate element and runs the risk of eroding the vertebral portion on which the tension is applied and/or the risk of the elongate element sliding on said vertebral portion.
In contrast with EP 1 933 743 B1, FR 2 981 841 A1 provides a tensioning ancillary instrument seeking to avoid the elongate element becoming twisted while it is being tensioned. The instrument thus includes a deflector so that the elongate element forms a 90° angle. The ends of the elongate element provided with securing means are fastened to a compensation wheel at two diametrically opposite points. The tension applied to each of the ends of the elongate element is thus not balanced. Furthermore, the deflector for deflecting the elongate element through 90° and the means for fastening one end in a cut gives rise to high level of friction on the elongate element, running the risk of weakening it. Furthermore, because of the deflector member, the instrument is bulky. Unfortunately, during surgery, many implants and longitudinal bars may be put into place on the vertebral level(s) for correction so that, once the elongate element has been put under tension, it is important for the surgeon to be able to have easy access to the implant in order to finish off tightening and fastening the implant on the elongate element, and also in order to have access to the other implants and/or longitudinal bars.